This project was initiated to study the role of catecholamines in the central and peripheral nervous system in experimental and genetic hypertension. Increased adrenaline formation has been demonstrated in specific brain areas of spontaneously hypertensive and doca-salt hypertensive rats. These changes coincide with changes in the formation of adrenaline in the adrenal medulla. Administration of inhibitors of adrenaline synthesis resulted in a normalization of the high blood pressure. During stress, similar changes in brain adrenaline are found in specific areas of the brain stem and hypothalamus. These findings suggest that localized areas in the rat brain and specific brain adrenergic neurons can play a role in the development of hypertension, in the stress reaction, and in the regulation of adrenomedullary catecholamine metabolism.